| | Case Introduction
Two Holstein fetuses aborted in fresh state at 8 months gestation; both were embryo transfers and implanted from the same flush into two dams. Dairy herd is well managed, well vaccinated and well fed. Gross necropsy was unremarkable except for a myocardial tear of unknown origin in one fetus.
Gross Findings
Both fetuses were aborted in fresh state. Both were small and fine-boned, weighing about 40 pounds, with no growth arrest lines seen. Postnatal breathes had not been taken. Thymus was obvious and well developed in both. One fetus had a full thickness myocardial tear in the left ventricular free wall, approximately 4 cm long.
Histopathology
Thyroid Glands: Lesions were seen in glands from both fetuses. One fetus showed complete lack of recognizable colloid within follicles. Follicles were lined by swollen cuboidal epithelial cells with pale wispy eosinophilic to vacuolated cytoplasm and intact but occasionally mildly pyknotic nuclei. Epithelial cells were sloughing into follicular lumens. The other fetus showed marked degenerative to necrotizing change with loss of acinar follicular architecture. Epithelial cells were sloughed with little recognizable basement membrane remaining. Cells had pale eosinophilic cytoplasm and nuclear changes varying from intense basophilia and shrinkage (pyknosis) to breaking apart to form small fragments of nuclear dust (karyorrhexis). Large irregular lakes of intensely basophilic material the size of 2 to 3 nuclei were also seen (nuclear aggregates).
Ancillary Tests
Special stains used to visualize lipofuscin were consistently negative in thyroid glands with this appearance. These included the more specific lipofuscin stains, like Schmorl’s, and less specific stains that may also help visualize lipochrome pigment, e.g. PAS and Fontana-Masson stains.
Morphological Diagnosis
Thyroid follicular epithelial degenerative to necrotizing change and sloughing with absence of colloid.
Etiological Diagnosis
Unknown.
Comments
The Western Canadian Beef Productivity Study (WCBPS) was done as a component of a larger study, Western Canada Study of Animal Health Effects Associated with Exposure to Emissions from Oil and Natural Gas Field Facilities. During the WCBPS, a very comprehensive set of tissues from calf death losses were examined histologically by Dr Ted Clark. Almost 1700 cases were examined, including 183 abortuses, 560 stillborn calves, 388 neonates and 558 calves > 3 days of age. Degenerative changes with or without necrosis that could not be attributed to autolysis were seen in thyroid glands of 16% of abortuses, 27% of stillborns, 22% of neonates and 17% of calves > 3 days of age1. Stillborn calves were significantly more likely to have lesions than neonates. Calves from young cows compared to older cows were less likely to have thyroid lesions. Liver selenium status was significantly associated with the odds of thyroid lesions. However, there was no clear relationship between increasing concentrations of liver selenium and decreasing odds of thyroid lesions. There was no association between liver vitamin E, copper or molybdenum status and thyroid lesions. Body condition score of the dam at pregnancy check and whether or not the birth was assisted were also not associated with thyroid lesions2.
References describing degenerative lesions with striking similarities to those seen in this series of calves have appeared in the human medical literature for many years3, 4. Controversy has centered on the significance of desquamation of cells into follicular lumina which many have considered a postmortem artifact. Some authors contend that degenerative changes that involve loss of colloid and follicular collapse are manifestations of normal hyperactivity as the thyroid gland undergoes a period of intense physiological activity to assist the newborn in adapting to extra-uterine life. There have been no associations made between maturity, age or sex of the fetus or between the presence or absence of pre-eclampsia, difficult labour or asphyxia and the thyroid lesions described. However, it remains unclear whether or not changes seen are pathological in some instances.
References
1. Western Interprovincial Scientific Studies Association. Research Appendices: Western Canada Study of Animal Health Effects Associated with Exposure to Emissions from Oil and Natural Gas Field Facilities: A Study of 33,000 Cattle in British Columbia, Alberta and Saskatchewan. January, 2006. [homepage on the internet]. Available from: http://www.wissa.info/index.html Last accessed 9/7/2008.
2. Dr. Cheryl Waldner, pers. comm.
3. Sclare G. The Histological Structure of the Thyroid in the Newborn. Scot Med J 1956;1:251-258.
4. Sagreiya K, Emery JL. Perinatal Thyroid Discharge: A Histological Study of 1225 Infant Thyroids. Arch Dis Child 1970;45:746–754.
E-mail: jan.bystrom@gov.ab.ca
Dr. Jan Bystrom, Veterinary Pathologist, Alberta Agriculture and Rural Development, Airdrie, AB, Dr. Ted Clark, C.A.R.E. Centre Animal Hospital, Calgary, AB |
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